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We present a model of vintage human capital. The economy exhibits exogenous deterministic technological change. Technology requires skills that are specific to the vintage. A stationary competitive equilibrium is defined and shown to exist and be unique, as well as Pareto optimal. The stationary equilibrium is characterized by an endogenous distribution of skilled workers across vintages. The distribution is shown to be single peaked, and under general conditions there is a lag between the time when a technology appears and the peak of its usage, what is known as diffusion. An increase in the rate of exogenous technological charge shirts the distribution of human capital to more recent vintages and increases the relative wage of the unskilled workers in each vintage.

'Structural unemployment' is said to occur in regions or 'sectors' of the economy as a consequence of technological changes. In this paper we present a model which provides an environment which gives rise to unemployment which could be labelled structural unemployment. There is exogenous technological change and vintage specific human capital. Unemployment arises as workers specialized in a particular technology within a vintage decide to search for a job within their vintage, so that their previously acquired special skills are used, instead of getting employed as unskilled workers in the newest vintage. As the rate of technological change increases, the incentives to reassign specialized workers to their same vintage, inccuring therefore in search costs, becomes less attractive, and in consequence the fraction of specialized workers doing search activities decreases. This provides some rationale for the negative correlation between rates of growth and unemployment observed in the data.

This paper develops a model of vintage human capital in which each technology requires vintage specific skills. We examine the properties of a stationary equilibrium for our economy. The stationary equilibrium is characterized by an endogenous distribution of skilled workers across vintages. The distribution is shown to be single peaked and, under general conditions, there is a lag between the time when a technology appears and the peak of it's usage, a phenomenon known as diffusion. An increase in the rate of exogenous technological change shifts the distribution of human capital to more recent vintages thereby increasing the diffusion rate.

This paper develops a model of vintage human capital in which each technology requires vintage specific skills. We examine the properties of a stationary equilibrium for our economy. The stationary equilibrium is characterized by an endogenous distribution of skilled workers across vintages. The distribution is shown to be single peaked and, under general conditions, there is a lag between the time when a technology appears and the peak of it's usage, a phenomenon known as diffusion. An increase in the rate of exogenous technological change shifts the distribution of human capital to more recent vintages thereby increasing the diffusion rate.

We present a model of vintage human capital. The economy exhibits exogenous deterministic technological change. Technology requires skills that are specific to the vintage. A stationary competitive equilibrium is defined and shown to exist and be unique, as well as Pareto optimal. The stationary equilibrium is characterized by an endogenous distribution of skilled workers across vintages. The distribution is shown to be single peaked and there is diffusion of technology in the sense that there is a lag between the time when a technology appears and the peak of its usage. An increase in the rate of exogenous technological change shifts the distribution of human capital to more recent vintages and increases the relative wage of the unskilled workers in each vintage.

We present a model of vintage human capital. The economy exhibits exogenous deterministic technological change. Technology requires skills that are specific to the vintage. A stationary competitive equilibrium is defined and shown to exist and be unique, as well as Pareto optimal. The stationary equilibrium is characterized by an endogenous distribution of skilled workers across vintages. The distribution is shown to be single peaked and there is diffusion of technology in the sense that there is a lag between the time when a technology appears and the peak of its usage. An increase in the rate of exogenous technological change shifts the distribution of human capital to more recent vintages and increases the relative wage of the unskilled workers in each vintage.

In this paper we analyze the constraints imposed by dynamic consistency in a model of optimal taxation. We assume that only distorting taxes are available to finance government consumption. Optimal fiscal policy requires the use of debt to smooth distortions over time. Dynamic consistency requires that governments at each point in time not have an incentive to default on the inherited debt. We consider policy functions which map the history of the economy including the actions of past governments into current decisions. A sustainable plan is a sequence of history-contingent policies which are optimal at each date given that future policies will be selected according to the plan. We show that if agents discount the future sufficiently little and if government consumption fluctuates then optimal sustainable plans yield policies and allocations which are identical to those under full commitment. We contrast our notion of dynamic consistency with other definitions.

In this paper we analyze the constraints imposed by dynamic consistency in a model of optimal taxation. We assume that only distorting taxes are available to finance government consumption. Optimal fiscal policy requires the use of debt to smooth distortions over time. Dynamic consistency requires that governments at each point in time not have an incentive to default on the inherited debt. We consider policy functions which map the history of the economy including the actions of past governments into current decisions. A sustainable plan is a sequence of history-contingent policies which are optimal at each date given that future policies will be selected according to the plan. We show that if agents discount the future sufficiently little and if government consumption fluctuates then optimal sustainable plans yield policies and allocations which are identical to those under full commitment. We contrast our notion of dynamic consistency with other definitions.